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JOHN R. MUELIN 



been invented. Some of them should be described briefly under the head- 

 ing of closed-circuit apparatus. 



An original form described bj Thunberg was a gas-analysis apparatus 

 of the Petterson type for the determination of very small percentages of 

 CO 2 in which the animals to be experimented on could be introduced into 

 the gas-measuring pipette. Any change in volume with the animal in the 

 confined space would be due to the difference between O 2 and CO 2 given 



Fig. 9. Micro-respiration apparatus of Winterstein. 5 and 6, duplicate air 

 chambers. The small animal is placed in chamber 6 and chamber 5 is used as control, 

 the two chambers being connected by a sensitive oil manometer. The absorption of 

 oxygen from chamber 6 is measured by the pressure of mercury necessary to restore 

 the balance on the oil manometer. 



off. This volume having been noted the air could then be driven over into 

 potash bulb and the CO 2 absorbed. Changes in volume this time would 

 give the CO 2 produced by the animal and the oxygen could be found by 

 adding the difference-volume first noted. 



Winter stein (a) improved upon this apparatus by employing the prin- 

 ciple of the compensating vessel first introduced into gas analysis by Petter- 

 son and connecting the two vessels (the animal chamber and compensating 

 chamber) by means of a very sensitive graduated manometer containing a 

 drop of kerosene. The oil-drop being set at zero, the level of the mercury in 

 the U-tube manometer at the left which is graduated in cubic millimeters is 



